By performing certain actions in Fever Mode, you'll unlock special achievements in the Results menu.

Achievement	How to unlock
Fever Mode Achievement #1	Clear Fever Mode.
Fever Mode Achievement #2	Score over 100,000 points.
Fever Mode Achievement #3	Score over 500,000 points.
Fever Mode Achievement #4	Score over 1,000,000 points.
Fever Mode Achievement #5	Complete Color Bonus.
Fever Mode Achievement #6	Played all Color Attack Colors.